ABB Relion 670 Series Applications Manual page 352

Section 13
Control
=
V
V
i Bmean
EQUATION1980-ANSI V1 EN-US
This value for the no-load voltage is then simply put into the voltage control function for single
transformer. There it is treated as the measured busbar voltage, and further control actions are
taken as described previously in section
doing this, the overall control strategy can be summarized as follows.
For the transformer producing/receiving the circulating current, the calculated no-load voltage
will be greater/smaller than the measured voltage V
be compared with the set voltage
will result in VLOWER or VRAISE being initiated alternatively. In this way the overall control action
will always be correct since the position of a tap changer is directly proportional to the
transformer no-load voltage. The sequence resets when V
same time as the calculated no-load voltages for all transformers in the parallel group are inside
the outer deadband.
In parallel operation with the circulating current method, different
transformers can cause the voltage regulation to be unstable. For this reason, the mean value of
VSet for parallel operating transformers can be automatically calculated and used for the voltage
regulation. This is set
VSet value is shown on the local HMI as a service value USETPAR under Main menu/Test/Function
status/Control/TransformerVoltageControl(ATCC,90)/TR8ATCC:x.
The use of mean
especially in cases when Load Voltage Adjustment is also used.
Line voltage drop compensation for parallel control
The line voltage drop compensation for a single transformer is described in section
drop". The same principle is used for parallel control with the circulating current method and with
the master – follower method, except that the total load current, I
instead of the individual transformer current. (See figure
parameters
change of these parameters due to changes in the substation topology, thus they should be
changed manually if needed.
Avoidance of simultaneous tapping
Avoidance of simultaneous tapping (operation with the circulating current method)
For some types of tap changers, especially older designs, an unexpected interruption of the
auxiliary voltage in the middle of a tap manoeuvre, can jam the tap changer. In order not to expose
more than one tap changer at a time, simultaneous tapping of parallel transformers (regulated
with the circulating current method) can be avoided. This is done by setting parameter
OperSimTap to On . Simultaneous tapping is then avoided at the same time as tapping actions (in
the long term) are distributed evenly amongst the parallel transformers.
The algorithm in Automatic voltage control for tap changer, parallel control TR8ATCC (90) will
select the transformer with the greatest voltage deviation V
then start timing, and after time delay
initiated. If now further tapping is required to bring the busbar voltage inside
the process will be repeated, and the transformer with the then greatest value of V
remaining transformers in the group will tap after a further time delay
possible as the calculation of I
346
+
V
di
VSet . A steady deviation which is outside the outer deadband
Enabled / Disabled by setting parameter OperUsetPar . The calculated mean
VSet is recommended for parallel operation with the circulating current method,
Rline and Xline shall be set in all IEDs in the same parallel group. There is no automatic
is cyclically updated with the most recent measured values. If two
cc
"Automatic voltage control for a single
. The calculated no-load voltage will then
Bmean
Bmean
166 for details). The same values for the
to tap first. That transformer will
di
t1 the appropriate VRAISE or VLOWER command will be
1MRK 511 358-UUS A
(Equation 124)
transformer". By
is inside the inner deadband at the
VSet values for individual
"Line voltage
, is used in the calculation
L
VDeadbandInner ,
amongst the
di
t2 , and so on. This is made
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